I'm asking this for a watercolor/cardmaker artist friend...she is looking for punches that will work on 140# paper...heavier than cardstock. I'm not familiar with that. Is she going to have to go with a die cutting machine and what kind?

Most bigger punches with not that much detailing, should work. I use nothing below 160gr and mine punch thru them. It's the thin papers that give me problems. The detailed punches wont work as they too fine but the basic shapes should be ok.
We have the Carl and Fiskars punches here and also the EK Success Whale punches along with some other store brand punches. Me mum is a punch fanatic and will create just about anything with them.

When not sure, go for the die cutting machines to be on the safe side.

I've broken more punches just using cardstock! (Especially Fiskars brand) I wish they would make something heavier. I'd be willing to pay a lot more per punch if I had something that would cut through cardstock without breaking.